We propose to continue our characterization of the experimental model of bladder cancer induced in Fischer rats by feeding N- 4-(5-nitro-2-furyl)-2-thiazolyl formamide (FANFT). Particular emphasis will be placed on determining the reversibility of the mucosal lesions, expanding our knowledge of dose and time relationships in the carcinogenic process, and the synergistic or co-carcinogenic effects of other agents given in addition to FANFT. Light microscopic and ultrastructural studies of bladder epithelium and tumors will be carried out in this model, and additional information will be collected concerning the late stages of the natural history of FANFT-induced bladder tumors in the Fischer rat. Efforts will be continued to develop transplantable lines of induced bladder tumors. BIBLIOGRAPHIC REFERENCES: Cohen, S.M., Jacobs, J., Friedell, G.H. and Russfield, A.B. Urinary bladder epithelial changes induced by N-(4-(5-nitro-2-furyl)-2-thiazolyl) formamide (FANFT) as observed by the scanning electron microscope (SEM.) Fed. Proc., 34: 828, 1975, abstract. Jacobs, J., Cohen, S.M., Arai, M. and Friedell, G.H. Scanning electron microscopy (SEM) observations of urinary cytology from rats fed N-(4-(5-nitro-2-furyl)-2-thiazolyl) formamide (FANFT). Proc. Amer. Assoc. Cancer Res. 16: 49, 1975, abstract.